Wafer and PCB warpage measurement starts with the datum

Keep the fixture state in the result definition.

Record whether the part is free, supported at specified locations, vacuum-chucked or clamped. A fixture can flatten the part or introduce a new shape, while a thin wafer or flexible PCB can sag under its own weight between supports. Use the same support, orientation, temperature and settling time when comparing the optical result with a reference method.

Define a datum from specified points or an agreed fitting method. Removing a best-fit plane removes rigid tilt; the remaining deviation still depends on the selected area and excluded features. Do not label a generic peak-to-valley surface result as a standards-compliant wafer bow, warp or flatness result without the required definition.

Turn distance readings into a registered height map.

A stationary point sensor returns one local distance. A surface map requires known XY motion or multiple measurement positions. Log encoder positions and acquisition times, then convert calibrated distances to height in the agreed coordinate system. Stage straightness, pitch and fixture motion can appear in the map.

Set the scan pitch from the smallest feature that must be resolved, not from the output resolution. State which pads, vias, edges, holes and component regions are included or masked. Keep a coverage map alongside the height map so missing readings are distinguishable from a flat surface.

For a 2D line scanner, one profile is a cross-section. Adding a controlled motion axis can build a surface map only if profiles are registered to motion. Check the usable X field at both Z extremes and define stitching where more than one pass is needed.

Review reflective and transparent wafers separately.

For a polished wafer, assess the incidence angle and available receive path across the complete scan. A valid reading at the center does not establish valid return at a bowed edge. Supply representative finish, coatings and expected slope to select the measurement arrangement.

Confocal and deflectometry are distinct alternatives used for different semiconductor tasks. The linked manufacturer overview illustrates this diversity. An LDS-CNF interest request initiates a technology review; it does not describe a released product or guarantee a transparent-layer measurement.